How to become friends with this girl, what do i do, say, i don't know her to well, what to say?

I have this problem to. I am attracted to depressed looking girls. There is a girl at my school who is a sophmore, and im a junior, anyways, she laughs and smiles and jokes with her friends, but shes friends with the wrong people. there have been times where i have just sat back and observed her with her friends. they are all the prepy type gossipy people, and she laughs, but i really pay attention, she shys away, and shes dresses differently and doesn't seem as if she belongs. she almost always has this blank, sorrowful expression on her face, I don't know what it is, but i can't get over her. i want to be friends with this girl. im intrigued by her, and want to get to know her better. i don't know what to say to her. she is friends with one of my friends, and he tells me about her, but he doesn't even know much, he doesn't see what i see. what do i say to her. my friend knows i like her alot and i think he has told her,he has a big mouth. anyways, yeah, what do i do?????????How to become friends with this girl, what do i do, say, i don't know her to well, what to say?
Well if she's looking depressed, pull her aside and ask her if something is wrong and if you could do anything about it. When she looks at you just kinda smile,or maybe wave. Or if you need help on an assignment you should ask her to help you so you guys could have a ';library date'; type thing.

Good Luck!How to become friends with this girl, what do i do, say, i don't know her to well, what to say?
Just ';run into her'; sometime.and start talking